Efficacy of Carotid Collateral Perfusion in Anaesthetized Sheep Fetuses

Rybakowski, C.; Eisermann, K.; Tchirikov, M.; Schröder, Helmut

doi:10.1053/plac.2000.0565

Cited by 1 publication

(2 citation statements)

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“…Based on an estimated carotid blood flow of 50 ml min −1 , which is in the range typical for this age of sheep fetus (Rybakowski et al . ), the nitrite infusions were predicted to increase carotid blood nitrite concentrations in half‐log increments from 0.020 to 66.6 μ m , the maximal concentration being approximately 20‐fold higher than physiological concentrations (Blood et al . ).…”

Section: Methodsmentioning

confidence: 99%

“…1). Based on an estimated carotid blood flow of 50 ml min −1 , which is in the range typical for this age of sheep fetus (Rybakowski et al 2000), the nitrite infusions were predicted to increase carotid blood nitrite concentrations in half-log increments from 0.020 to 66.6 μM, the maximal concentration being approximately 20-fold higher than physiological concentrations (Blood et al 2009). Arterial and venous blood samples for blood gas analysis and haemoximetry (ABL-800, Radiometer, Copenhagen, Denmark) and measurement of nitrite concentrations were drawn every 30 min until completion of nitrite or saline infusions, and 15 and 45 min afterward.…”

Section: Nitrite Infusionmentioning

confidence: 99%

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Role of nitrite in regulation of fetal cephalic circulation in sheep

Truong¹,

Schröder

Liu

et al. 2014

The Journal of Physiology

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Key pointsr Recent evidence in adult humans demonstrates that nitrite, at physiological concentrations, can be converted into vasodilating amounts of NO, thus constituting an alternative to NO production by NO synthases.r Nitrite reacts with deoxyhaemoglobin to produce NO, a reaction proposed to mediate the vasodilating effects of nitrite. We have demonstrated previously that the rate of this reaction is ß2-fold faster with fetal haemoglobin than adult haemoglobin. Thus, we hypothesized that nitrite would be a potent vasodilator in the cephalic vasculature served by the carotid artery in the fetal sheep.r In conflict with human adult forearm studies, we find that nitrite is not a vasodilator in the fetal sheep cephalic vasculature, despite the fact that nitrite is converted to NO more efficiently by fetal haemoglobin.r The results suggest that the vasodilatory effects of nitrite are age-and species-specific, and that the reaction of nitrite with deoxyhaemoglobin is not rate limiting with respect to its ability to decrease vascular tone.Abstract Nitrite has been postulated to provide a reservoir for conversion to nitric oxide (NO), especially in tissues with reduced oxygen levels as in the fetus. Nitrite would thus provide local vasodilatation and restore a balance between oxygen supply and need, a putative mechanism of importance especially in the brain. The current experiments test the hypothesis that exogenous nitrite acts as a vasodilator in the cephalic vasculature of the intact, near term fetal sheep. Fetuses were first instrumented to measure arterial blood pressure and carotid artery blood flow and then studied 4-5 days later while in utero without anaesthesia. Initially L-nitro-arginine (LNNA) was given to block endogenous NO production. Carotid resistance to flow increased 2-fold from 0.54 ± 0.01 (SEM) to 1.20 ± 0.08 mmHg min ml −1 (in 13 fetuses, P < 0.001), indicating NO tonically reduces cerebral vascular tone. Sodium nitrite (or saline as control) was then infused in increasing step-doses from 0.01 to 33 μM in half-log increments over a period of 2 h. Carotid artery pressure, blood flow and vascular resistance did not change compared to fetuses receiving saline, even at plasma nitrite concentrations two orders of magnitude above the physiological range. The results indicate that while cephalic vascular tone is controlled by endogenous nitric oxide synthase activity, exogenously administered nitrite is not a vasodilator at physiological concentrations in the vasculature served by the carotid artery of fetal sheep.

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Section: Methodsmentioning

confidence: 99%

Section: Nitrite Infusionmentioning

confidence: 99%